Hydrogen abstraction from toluene by methyl radicals and the pressure dependence of the recombination of methyl radicals

Self Cite

The pyrolysis of diethylmercury has been studied in a toluene carrier flow system from 601 to 673 "K using total pressures of 1.04 to 7.75 mm. The progress of the reaction was followed by measuring the amounts of unreacted alkyl. Partial solution of butane in the toluene condensed at the outlet of the reactor made full product analysis difficult. Complete analysis in a number of runs did yield a good material balance between alkyl decomposed and C4Hlo + f(C2Hs + C2H4 + n-propylbenzene). IHg (CzH5) 2CzH5 + CzH4 + CzHs The Arrhenius equation for reaction 1, log kl(s-') = 15.4 -(45 700 + 1 000)/2.3 RT, is in excellent agreement with that estimated by Benson and O'Neal. Based on a number of simplifying approximations, log k,(cm3 mol-' s-') = 10.9 -(9 300 rt 2 000)/2.3 RT. The estimated disproportionation to combination ratio, k5/k4 = 0.09 -0.12 is in good agreement with earlier work.Approximate correction of El to absolute zero yields D(CzH5Hg-CzH5) = 43.7 kcal mol-I and therefore by difference D(Hg-C2H5) = 6.5 kcal mol-l.La pyrolyse du diBthylmercure a Ct B Btudiie dans un systtme ou le courant porteur est le tolutne, entre 601 et 673 "K et en utilisant des pressions totales de 1.04 a 7.75 mm. L'avancement de la reaction est suivie en mesurant la quantite d'alkyle n'ayant pas rkagi. La condensation de solution de butane dans le tolutne, a la sortie du reacteur, rend dificile I'analyse compltte des produits. L'analyse compltte sur plusieurs essais, donne un bon Cquilibre au point de vue produit entre la decomposition de I'alkyle et C4H10 + 3(CZH6 + CZH4 + n-propylbenzene) approximatives log k3 (cm3 mol-Is-') = 10.9 -(9 300 + 2 000)/2.3RT. L'estimation du rapport dismutation sur combinaison, k5/k4 = 0.09 -0.12 est en bon accord avec un travail prkckdent.L'extrapolation approximative de El ou zero absolu donne D(C2H5Hg-C2H5) = 43.7 kcal mol-l d'ob par diffkrence D(Hg-C2H5) = 6.5 kcal mol-'.

Section: Resultsmentioning

confidence: 70%

Determination of the Bond Dissociation Energy D(C₂H₅Hg—C₂H₅) by the Toluene Carrier Method

Lalonde¹,

Price²

1971

Self Cite

“…9 and the measurements are summarized in Table 3, which includes the ratios of rate constants k15/k3 and k16/k4 obtained from eqs. [17] and [18]. The Arrhenius plots for kI5/k3 and k16/k4 are shown in Fig.…”

Section: Cyclopentanementioning

confidence: 99%

Rate constants for abstraction of hydrogen from benzene, toluene, and cyclopentane by methyl and ethyl radicals over the temperature range 650–770 K

Zhang¹,

Ahonkhai²,

Back³

1989

. Can. J. Chem. 67, 1541 (1989). Rate constants for the abstraction of hydrogen from benzene, toluene, and cyclopentane by methyl and ethyl radicals have been measured relative to the corresponding abstraction reaction from ethylene. The method is based on the effect on the rates of formation of methane and ethane of the addition of small quantities of the reactants to the thermal chain reactions of ethylene in the temperature range 650-770 K. Taking the following values of the rate constants for the reference reactions (R = 8.314 J mol-' K-I):[4] C2Hs + C2H4 -* C2H6 + C2H3; log k4 (L mol-' s-I) = 8.2 t-0.2 -(62200 t-3000)/2.3RT the following rate constants were measured:[8] C2Hs + C6H6 -* C2H6 + C6HS; log kg (~m 0 1 -' S-') = 8.8 i 0.3 -(62200 i 5000)/2.3RT [ l l ] CH3 + C7Hg + CH4 + C7H7; log kll (L mol-' s-') = 7.4 i 0.5 -(29000 ? 7000)/2.3RT[12] C2HS + C7H8 'C2H6 + C7H7; log k12 ( L m~l -' s -~) = 7.7 * 0.5 -(37000 ? 7000)/2.3RT[15] CH3 + c-CsHlo -CH4 + c-C5Hg; log klS (L mol-' s-I) = 8.3 2 0.5 * (36000 ?7000)/2.3RTThe values of the activation energies are discussed in relation to the dissociation energies of the C-H bonds in the reactants.

“…Also, no allowance has been made for that fraction of the recombination product which undergoes subsequent redissociation. Another major correction is required because recent work from this laboratory on the recombination of methyl radicals (8) indicates that our published values for log k-, are too high by about 0.15 log units. The exact correction that should be made to E, is uncertain.…”

Section: 5mentioning

confidence: 99%

Free-radical and molecular processes in the pyrolysis of ethylbenzene

Clark¹,

Price²

1970

From 910 to 1089°K, at pressures of 20 to 36 mm, the pyrolysis of ethylbenzene in a toluene carrier flow system occurs primarily by three reactions[Formula: see text]The Arrhenius equation for the reaction [1], log k1 (s−1) = 14.7 − (70 100/2.3RT), is in agreement with a previous aniline carrier study and with thermochemical calculations. Reaction [11] is surface dependent and yields widely scattered results. For experiments in a conditioned quartz vessel, log k11 (s−1) = 9.06 − (51 700/2.3RT). Values of k1and k12 are unaffected by the nature of the surface and by changes in the surface-to-volume ratio. The rate constants for reaction [12] are somewhat scattered, but yield the approximate equation log k12 (s−1) = 12.7 − (64 000/2.3RT).E1 should possibly be increased by about 1 kcal to allow for the effect of reaction [−1], the recombination of methyl and benzyl species.